Open Ended D10

Here I present a game mechanics idea I have for a possible game system I might do some day in the future. Things never get done until you write them down, so I decided to include it here in the wiki. You're all of course invited to use it in your own games and tweak it as you like.

I just want to take the typical d100 roll you find in Runequest (with critical hit and miss) and the open ended d100 roll in Rolemaster (with an infinite array of results) and meld them into a d10 roll. I find d100 rolls a mess because rolling two dice at the same time usually means that they scatter all around the table and floor, and they make calculations (as including modifiers or determining success) more difficult without actually adding anything in return.

Enrique Martín, 2006.

Rolling the die

You have an attribute/skill/whatever usually ranging from 1 to 8 that you need to test in a given situation. You roll one standard ten-sided die :

• If you roll a number from 1 to 9 you compare it with your attribute.
  • If you roll less or equal than your attribute you get a success.
  • If you roll more than you attribute you get a failure.
• However, if you roll a 0 (also labelled 10 in some d10 dice) you get a critical result, which can be either very good or very bad. To determine it you have to roll a second die.
  • If you roll a number from 1 to 9 you compare it with your attribute.
    • If you roll less or equal than your attribute you get a critical success.
    • If you roll more than you attribute you get a critical failure.
  • If you roll 0 again you get a double critical result. Rolling a third die will determine whether it is a double critical success or a double critical failure. Of course getting more 0's would yield triple criticals, cuadruple criticals and so on.

Properties

The open-ended d10 roll is technically equivalent to the Runequest d100 roll where a score of 1 would become a 10%, a score of 2 a 20% and so on. Everytime there is a 10% probability of getting a critical result, just in Runequest (for example, if you had a 40% you would get a critical sucess with 01-04 and a critical failure with 95-100 in your d100 roll, it is the same probability-wise).

There is also a resemblance with the Rolemaster open-ended d100 as double (1% chance), triple (1 in 1000 chance), cuadruple (1 in 10.000 chance), etc. criticals can be generated, so truly glorious rolls can happen.

Automatical success and failure rule

The die roll represents how well or bad the character fares using his existing attribute in a given situation. But sometimes external unpredictable events can determine the outcome in spite of the character effort and skill.

If a 0 is rolled (critical result), then :
• If you roll a 1 you get a lucky success regardless of your attribute score.
• If you roll a 9 you get a lucky failure regardless of your attribute score.
• If you roll a 0 (double critical result) you can then get double lucky success by rolling a 1 or double lucky failure rolling a 9, and so on.

With this rule characters can get a success even with 0 or below attribute scores (1% chance). Exceptional characters (9 or greater attribute score) can still fail (1% chance), just like in Runequest.

Simple roll

Sometimes you just need to know if the task is performed or not, without caring about critical or lucky results. In that case make a simple roll by ignoring any 0's you get, just roll again. If your attribute score is 0 or less you don't need to roll because you fail automatically; similiarly, if it is 9 or greater you are automatically succesful. This can speed things up with routinary tasks.

Degree of Success

On the other hand, sometimes you need to gauge how well you perform a task, for example when you compete against other character (as in 'he who throws the stone further wins'). A critical success is always better than a regular success (and a double critical better than a regular critical, etc.) as it is to be expected, but you can also compare two successes against each other, the greater the roll the better the task is performed.

In fact, if you get a success the number you get in the die is called the degree of success, which you can compare against your opponent's degree or even against a difficulty degree set by the Game Master. If you get a critical success your roll is called degree of critical success and so on. Even a degree of failure can be considered when opportune, the lower the degree the worse the failure is.

Beyond Success

In a roleplaying game sometimes truly amazing and extraordinary challenges await the main characters. The Game Master can require a critical success or even a double or greater critical success in order to achieve such deeds. Be aware that your chances of getting a double critical success are only 1 tenth of getting a critical success, and that is 1 tenth of getting a success, so they're dropping exponentially.

Great tasks thus require great skill in the form of mastery ranks, each of which allows to shift a failure into a success, a success into a critical success and so on. You can write a star(*) after the attribute score to represent each rank in a character sheet.